This application claims the benefit of the Korean Application No. P2000-72707 filed on Dec. 02, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal projector, and more particularly, to an optical system of a liquid crystal projector with three reflective liquid crystal displays.
2. Background of the Related Art
Recently, as demands on large sized, and high resolution pictures become the stronger, projectors are paid attention as displays, for making enlargement projection of a picture by means of a projection lens system. The picture may be projected in front or rear direction.
The liquid crystal projector projects a light from a light source to a liquid crystal panel, and therefrom to a screen by means of a projection optical system. When the picture is projected to the screen in rear of the liquid crystal panel directly, a distance of projection distance between the screen and the projection optical system requires a large space in rear of the screen, to make the projector thick, that impedes fabrication of a thin projector.
As a solution for this problem, a total reflection mirror may be provided between the screen and the projection optical system, to fold an optical path, that can reduce the thickness of the projector. In this instance, though the thickness of the projector may be reduced further by reducing an angle of dispose of the total reflection mirror, there has been a limit in the angle of dispose between the mirror and the projection optical system for projection of the picture on the screen without distortion, and there has been a limitation in reduction of a system thickness coming from intrinsically required total length of an optical system consisting of a lighting system, the liquid crystal panel, and the projection lens system.
Accordingly, there have been various plans for reducing the total length of the optical system. FIG. 1 illustrates a related art optical system of a liquid crystal projector, employing a polarizing beam sprite prism which reflects, or transmits an incident light depending on a wavelength and a direction of polarization, for reducing a total length of the optical system.
In detail, the optical system in FIG. 1 is provided with a fly eye lens (FEL) 42 between a light source 40 and a first total reflection mirror 44, and a second FEL 46, a polarizing beam sprite array (PBS array) 47, and a focusing lens 48 between the first total reflection mirror 44 and a second total reflection mirror 50.
The optical system of a liquid crystal projector in FIG. 1 is further provided with a dichroic mirror 52 on an optical path of a light reflected at the second total reflection mirror 50, a first polarizing beam sprite prism (PBSP) 54A on an optical path between the first dichroic mirror 52 and a blue liquid crystal panel 56A, a second PBSP 54B on an optical path between the first dichroic mirror 52 and a green liquid crystal panel 56B, a first relay lens 60, a third total reflection mirror 62, a second relay lens 64, fourth, and fifth total reflection mirrors 66 and 68, a third PBSP 54C on an optical path between the second PBSP 54B and a red liquid crystal panel 56C, a dichroic prism 70 among the first, to third PBSPs 54A, 54B, and 54C, and a projection lens 72 opposite to a light projecting surface of the dichroic prism 70.
Since the second PBSP 54B can separate colors, the foregoing optical system can reduce a number of dichroic mirrors, to reduce a total length of the optical system. In this instance, a red light passed through the second PBSP 54B proceeds along an optical path that is turned in a form surrounding the third liquid crystal panel 56C by the fourth to sixth total reflection mirrors 62, 66, and 68, and is directed to the third liquid crystal panel 56C.
In the meantime, in general, a connector 10 is fitted at a side of the third liquid crystal panel, 56C i.e., at a bottom thereof in FIG. 1 for connecting the third liquid crystal panel 56C to external signal lines, causing an interference with the path of the red light. Accordingly, as the path of the red light is required to be spaced away from the connector 10 of the third liquid crystal panel 56C as far as possible, there is a limitation in reducing the total length of the optical system.
Accordingly, the present invention is directed to an optical system of a liquid crystal projector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an optical system of a liquid crystal projector, in which a total length of the optical system is reduced to reduce a thickness of an entire system.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the optical system of a liquid crystal projector for superimposing, enlarging, and projecting pictures displayed on first to third liquid crystal panels by using color lights received through first to third light path changing parts, wherein the first light path changing part includes a first sub-light path part for making a first time alteration of a linearly polarized light component of the color light received from one of the first to third light path changing parts, a second sub-light path part for reflecting the color light from the first sub-light path part, and making a second alteration of the linearly polarized component of a reflected color light, and forwarding to the first sub-light path part, and a third sub-light path part for directing the color light received through the second sub-light path part and the first sub-light path part to the first liquid crystal panel relevant to the color light, wherein the first to third sub-light path parts are arranged spaced away from the first liquid crystal panel, on sides of the first liquid crystal panel respectively except a side the connector is fitted thereto.
The first sub-light path part includes a first xcex/2 plate for altering a linearly polarized component of a color light received from one of the second, and third light path changing parts, the second sub-light path part includes a first total reflection mirror for reflecting the color light from the second sub-light path part at a right angle, a second total reflection mirror for reflecting back the color light from the first total reflection mirror, a xcex/4 plate for altering a first linearly polarized light in one direction from the first total reflection mirror to a circular polarized light and forwarding the circular polarized light, and altering a circular polarized light from the second total reflection mirror to a second linearly polarized light in the other direction, and forwarding the second linearly polarized light, and the third sub-light path part includes a first polarizing beam sprite prism (PBSP) for transmitting the first linearly polarized light from the first xcex/2 plate toward the first total reflection mirror, and reflecting the second linearly polarized light from the first total reflection mirror at a right angle, a second PBSP for reflecting the second linearly polarized light from the first PBSP toward the first liquid crystal panel at a right angle, and a second xcex/2 plate for altering the first linearly polarized light from the second PBSP to a second linearly polarized light.
The first, second, and third sub-light path parts further includes at least one refractive lens for preventing light scattering and relaying an image forming point, and the refractive lens in the first sub-light path part is arranged between the first xcex/2 plate and the first PBSP, the refractive lens in the second sub-light path part is arranged between the xcex/4 plate and the second total reflection mirror, and the refractive lens in the third sub-light path part is arranged between the first PBSP and the second PBSP.
The second sub-light path part further includes a color filter for enhancing a purity of the color light, and the color filter is arranged between the xcex/4 plate and the second total reflection mirror.
The xcex/4 plate is arranged between the first total reflection mirror and the second total reflection mirror, the first PBSP is arranged between the first xcex/2 plate and the first total reflection mirror, and the second PBSP is arranged between the first liquid crystal panel and the second xcex/2 plate.
In another aspect of the present invention, there is provided an optical system of a liquid crystal projector for superimposing, enlarging, and projecting pictures displayed on first to third liquid crystal panels including a light source, an illuminating part for altering a white light from the light source to a linearly polarized light, and forwarding the linearly polarized light, a color separating part for separating the white color from the illuminating part into first to third color lights, a third light path changing part for reflecting the three color lights to the third liquid crystal panel, a second light path changing part for reflecting two color lights received through the third light path changing part to the second liquid crystal panel, and a first light path changing part including a first sub-light path part for making a first time alteration of a linearly polarized light component of the first color light received from the second light path changing part, a second sub-light path part for reflecting the first color light from the first sub-light path part, and making a second alteration of the linearly polarized component of a reflected first color light, and forwarding to the first sub-light path part, and a third sub-light path part for directing the first color light received through the second sub-light path part and the first sub-light path part to the first liquid crystal panel, wherein the first to third sub-light path parts are arranged spaced away from the first liquid crystal panel, on sides of the first liquid crystal panel respectively except a side the connector is fitted thereto.
In the first light path changing part, the first sub-light path part includes a first xcex/2 plate for altering a linearly polarized component of a color light received from one of the second, and third light path changing parts, the second sub-light path part includes a first total reflection mirror for reflecting the color light from the second sub-light path part at a right angle, a second total reflection mirror for reflecting back the color light from the first total reflection mirror, a xcex/4 plate for altering a first linearly polarized light in one direction from the first total reflection mirror to a circular polarized light and forwarding the circular polarized light, and altering a circular polarized light from the second total reflection mirror to a second linearly polarized light in the other direction, and forwarding the second linearly polarized light, and the third sub-light path part includes a first polarizing beam sprite prism (PBSP) for transmitting the first linearly polarized light from the first xcex/2 plate toward the first total reflection mirror, and reflecting the second linearly polarized light from the first total reflection mirror at a right angle, a second PBSP for reflecting the second linearly polarized light from the first PBSP toward the first liquid crystal panel at a right angle, and a second xcex/2 plate for altering the first linearly polarized light from the second PBSP to a second linearly polarized light.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.